Calculation of stress intensity factor for functionally graded cylinders with two radial cracks using the weight function method

, Article Theoretical and Applied Fracture Mechanics ; Volume 85 , 2016 , Pages 447-456 ; 01678442 (ISSN) Mirahmadi, H ; Azimi, M ; Mirjavadi, S. S ; Sharif University of Technology

Elsevier B.V 2016

Abstract

In this study, obtaining stress intensity factors (SIFs) for functionally graded cylinders with two internal radial cracks using the weight function method has been discussed. For this purpose, reference SIFs are calculated from the results of finite element analysis, using a modified domain of the J integral. Subsequently, SIFs have been calculated for different combinations of cylinder geometry, crack depth, and material gradation by implementing the weight function method and it is shown that the results are consistent with corresponding results obtained from finite element analysis. Moreover, the effects of variation in the elastic modulus ratio on SIFs have been investigated. © 2016...

Investigating the Mathematical Model of Transformers in Deep Learning Using the Self-Attention Mechanism in Multi-Layer Neural Networks

, M.Sc. Thesis Sharif University of Technology Mirjavadi, Mojtaba (Author) ; Bahraini, Alireza (Supervisor) ; Shams Yousefi, Marzieh (Supervisor)

Abstract

This dissertation is organized into three chapters. The first chapter presents the necessary concepts and theorems. The second chapter addresses the primary objectives of the study. The third chapter is devoted to the proof and analysis of the convergence theorem for the attention matrix to low-rank Boolean matrices. The objective of this thesis is to investigate the mathematical model of the selfattention mechanism in deep learning, which is examined through the lens of optimal transport theory. It includes two theorems concerning clustering and the convergence of solutions to the differential equation describing the self-attention mechanism.

Thermal buckling behavior of two-dimensional imperfect functionally graded microscale-tapered porous beam

, Article Journal of Thermal Stresses ; Volume 40, Issue 10 , 2017 , Pages 1201-1214 ; 01495739 (ISSN) Mirjavadi, S. S ; Matin, A ; Shafiei, N ; Rabby, S ; Mohasel Afshari, B ; Sharif University of Technology

2017

Abstract

This article presents a study on the thermal buckling behavior of two-dimensional functionally graded microbeams made of porous materials. The material composition varies along thickness and length of the microbeam based on the power law distribution. The microbeam is modeled within the framework of Euler–Bernoulli beam theory. The microbeam is considered having variable material composition along thickness. The equations are derived using the modified couple stress theory and the solving process is based on the generalized differential quadrature method. The validity of the results is shown through comparison of the results with the results of other published research. © 2017 Taylor &...

On size-dependent free vibration and thermal buckling of axially functionally graded nanobeams in thermal environment

, Article Applied Physics A: Materials Science and Processing ; Volume 123, Issue 5 , 2017 , 315 ; 09478396 (ISSN) Mirjavadi, S. S ; Rabby, S ; Shafiei, N ; Mohasel Afshari, B ; Kazemi, M ; Sharif University of Technology

Springer Verlag 2017

Abstract

This article aims to study the buckling and free vibrational behavior of axially functionally graded (AFG) nanobeam under thermal effect for the first time. The temperature is considered to be constant and variable along thickness and different boundary conditions. The governing equation is developed using the Hamilton’s principle considering the axial force. The Euler–Bernoulli beam theory is used to model the nanobeam, and Eringen’s nonlocal elasticity theory is utilized to consider the nano-size effect. The generalized differential quadrature method (GDQM) is used to solve the equations. The small-scale parameter, AFG power index, thermal distribution, different functions of temperature...

Transient response of porous FG nanoplates subjected to various pulse loads based on nonlocal stress-strain gradient theory

, Article European Journal of Mechanics, A/Solids ; Volume 74 , 2019 , Pages 210-220 ; 09977538 (ISSN) Mirjavadi, S ; Mohasel Afshari, B ; Barati, M. R ; Hamouda, A. M. S ; Sharif University of Technology

Elsevier Ltd 2019

Abstract

Based on nonlocal strain gradient theory (NSGT), transient behavior of a porous functionally graded (FG) nanoplate due to various impulse loads has been studied. The porous nanoplate has evenly and unevenly distributed pores inside its material structure. Impulse point loads are considered to be rectangular, triangular and sinusoidal types. These impulse loads lead to transient vibration of the nanoplate which is not studied before. NSGT introduces a nonlocal coefficient together with a strain gradient coefficient to characterize small size influences due to non-uniform stress and strain fields. Galerkin's approach has been performed to solve the governing equations and also inverse Laplace...

Effect of temperature and porosity on the vibration behavior of two-dimensional functionally graded micro-scale timoshenko beam

, Article JVC/Journal of Vibration and Control ; Volume 24, Issue 18 , 2018 , Pages 4211-4225 ; 10775463 (ISSN) Mirjavadi, S. S ; Mohasel Afshari, B ; Shafiei, N ; Rabby, S ; Kazemi, M ; Sharif University of Technology

2018

Abstract

This work is aimed to present analysis on the thermal vibrational behavior of two-dimensional functionally graded porous microbeams based on Timoshenko beam theory. According to the power law function, the material composition and so the material properties are varying along thickness and axis of the microbeam. The governing equations are derived on the basis of the couple stress theory and the generalized differential quadrature method is used to solve the equations. The temperature gradient is considered to be uniform and nonuniform across the thickness of the microbeam. The results are presented to show the effect of temperature change, porosity, functionally graded and axially...

Preparation, Surface Modification and Application of Nanocomposite Membranes Based on Transition Metals- Dichalcogenide Nanoparticles in Forward Osmosis Desalination Process

, Ph.D. Dissertation Sharif University of Technology Nikkhoo, Mohammad (Author) ; Bagherzadeh, Mojtaba (Supervisor) ; Ahadian, Mohammad Mahdi (Supervisor) ; Amini, Mojtaba (Supervisor)

Abstract

Different parts of this research are focused on developing FO membranes and improving their performance. For this purpose, thin film composite (TFC) membranes with fixed composition of polyethersulfone/polyamide (PES/PA) have been used to investigate the effect of nanocomposites containing transition metal dichalcogenides (TMDs) on their performance. The support layer in all cases is PES, which is prepared through the phase inversion process and does not contain any nanofillers. The modification process takes place in the polyamide layer by dispersing the desired nanoparticles in the aqueous monomer solution necessary to form this active layer. Identification and characterization of...

Correlating the microstructure to mechanical properties and wear behavior of an accumulative back extruded Al-Mg2Si in-situ composite

, Article Tribology International ; Volume 115 , 2017 , Pages 199-211 ; 0301679X (ISSN) Ebrahimi, M ; Zarei Hanzaki, A ; Abedi, H. R ; Azimi, M ; Mirjavadi, S. S ; Sharif University of Technology

Elsevier Ltd 2017

Abstract

The present work was conducted to study the effects of microstructural evolutions on the mechanical and wear behavior of an accumulative back extruded aluminum-based in-situ composite. The mechanical fragmentation and thermal disintegration of the primary and secondary Mg2Si particles were found as the main microstructural changes. For that reason, the particle interspacing was decreased, the sharp ends were modified, and the reinforcements were more uniformly distributed. Surprisingly, the wear loss was dramatically decreased in processed materials in comparison to the as-received one. Oxidation and delamination were identified as the dominant wear mechanisms. These were addressed...

Nonlinear free and forced vibrations of graphene nanoplatelet reinforced microbeams with geometrical imperfection

, Article Microsystem Technologies ; Volume 25, Issue 8 , 2019 , Pages 3137-3150 ; 09467076 (ISSN) Mirjavadi, S. S ; Mohasel Afshari, B ; Barati, M. R ; Hamouda, A. M. S ; Sharif University of Technology

Springer Verlag 2019

Abstract

Nonlinear free/forced vibration of a functionally graded graphene nanoplatelet (GNP) reinforced microbeam having geometrical imperfection which is rested on a non-linear elastic substrate have been studied in the present research. Graphene Platelets have been uniformly and non-uniformly scattered in the cross section area of the microbeam. Non-uniform distribution of GNPs is considered to be linear or non-linear type. Geometric imperfection is considered similar to the first vibration mode of microbeam. Size effects due to micro-rotations are captured in this study by means of modified couple stress elasticity. In the case of forced vibration, a uniform harmonic load is exerted to the top...

Transient response of porous inhomogeneous nanobeams due to various impulsive loads based on nonlocal strain gradient elasticity

, Article International Journal of Mechanics and Materials in Design ; Volume 16, Issue 1 , March , 2020 , Pages 57-68 Mirjavadi, S. S ; Mohasel Afshari, B ; Barati, M. R ; Hamouda, A. M. S ; Sharif University of Technology

Springer 2020

Abstract

Transient vibration responses of a porosity-dependent functionally graded nanobeam under different impulsive loadings have been investigated in the context of non-local strain gradient theory. Three impulse loads of rectangular-type, linear-type and sine-type have been applied to top surface of nanobeam. Two porosity distribution types known as even and uneven are discussed. Governing equations of the nanobeam are solved via inverse Laplace transform approach to express the dynamic deflections. One can see that the transient response of nano-size beams is influenced by the type and location of pulse load, porosities volume fractions, porosities distributions, non-local and strain gradient...

Strain gradient based dynamic response analysis of heterogeneous cylindrical microshells with porosities under a moving load

, Article Materials Research Express ; Volume 6, Issue 3 , 2019 ; 20531591 (ISSN) Mirjavadi, S. S ; Mohasel Afshari, B ; Barati, M. R ; Hamouda, A. M. S ; Sharif University of Technology

Institute of Physics Publishing 2019

Abstract

Forced vibration of a porous functionally graded (FG) cylindrical microshell due to a moving point load with constant velocity is studied for the first time. Through the thickness of microshell, there are even-type or uneven-type porosities. Therefore, material properties of the microshell become porosity-dependent and are described via modified power-law function. For micro-scale shells, small size effects due to non-uniform strain field can be considered via strain gradient theory (SGT). At first, the governing equations of the microshell are converted to new equations in Laplace domain. Then, time response of the microshell will be obtained implementing inverse Laplace transform...

Synthesis, Structure and Catalytic Application of Mn, Fe and Mo Complexes with Schiff base and Oxazoline ligands and Theoretical Mechanistic Studies on the Role of Heme and non-Heme Iron(IV)-Oxo Species in Hydroxylation and Epoxidation Reactions

, Ph.D. Dissertation Sharif University of Technology Tahsini , Laleh (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

The first part of this thesis describes the synthesis and characterization of several Mn, Fe and Mo complexes containing tridentate Schiff base and oxazoline ligands and their reactivities as catalysts in the oxidation of organic compounds like olefins and sulfides, as well. The crystal structures of newly prepared cis-dioxo-bis[2-(2′-hydroxyphenyl)-oxazolinato]molybdenum(VI), cis-[MoO2(phox)2] and (N-hydroxyphenyl-salicylidenamine)(acetylacetonato)ethanol iron(III), [FeIII(N-OPh-sal)(acac)EtOH] complexes have been described by X-ray crystallography. Due to the difficulties in the preparation of suitable single crystals of novel...

Design and Fabrication of RFID Front END Transceiver single chip with 2.5W Output Power

, Ph.D. Dissertation Sharif University of Technology Javidan, Javad (Author) ; Atarodi, Mojtaba (Supervisor)

Abstract

This thesis deals with the front-End of an Integrated RFID Reader operated in 860MHz to 960MHz, which integrates a RF transceiver including PA, LNA and Mixer. In the receiver part, a power amplifier was fabricated and measured and in the transmitter part, LNA and Mixer were designed. There is a growing interest in utilizing CMOS technologies for RF power amplifiers (PAs). Although several advances have been made recently to enable full integration of PAs in CMOS, it is still among the most difficult challenges in achieving a truly single-chip radio system in CMOS. This is exacerbated by supply voltage reduction due to CMOS technology scaling and on-chip passive losses due to the conductive...

, M.Sc. Thesis Sharif University of Technology Hatami, Mojgan (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

Inert gold become catalytically active when dispersed in the form of nanoparticles. Isolated gold nanoparticles have demonstrated high catalytic activity for both oxidation and reduction reactions. In order to obtain high catalytic activity, gold nanoparticles are generally dispersed on support materials, among which oxides are commonly used. However, a substantial decrease in activity and selectivity of the immobilized catalysts is frequently observed due to the heterogeneous nature of these support materials in reaction media. In the course of our study on the metal-based catalysis for synthesis of organic compounds, we herein report that rod-shaped Au nanoparticles in aqua solution...

Synthesis and Characterization of a novel Ruthenium(II) Complex With Bidentate O,N-donor OxazolineLigand and Study of Catalytic Oxidation of Sulfides and Alkanes

, M.Sc. Thesis Sharif University of Technology Hosseini, Mojtaba (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

The 2-(2′-hydroxyphenyl)-oxazoline ligand (Hphox) is generated from 1:1 condensation of methyl salicylate with 2-aminoethanol. Novel [Ru(Hphox)2(H2O)2] (Hphox = 2-(2′-hydroxyphenyl)-oxazoline ) complex has been synthesized and characterized by physic-chemical methods. Oxidation of sulfides catalyzed by the mixed-ligand ruthenium(II) complex [Ru(Hphox)2(H2O)2]using urea-hydrogen peroxide (UHP) as oxidant was investigated under mild condition within 1 h. The results showed that mixed-ligand ruthenium(II) complex was effective catalyst in oxidation of sulfides in whichsulfoxideswere the only products. Using this catalytic system in the oxidation of alkanes, ketones were obtained as the main...

Synthesis of Core-Shell Nanoparticles Supported Iron and Vanadium Schiff Base and Their Application as a Catalyst for Oxidation of Sulfides, Alcohols and Olefins

, M.Sc. Thesis Sharif University of Technology Payab, Ebrahim (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

In this work, synthesized Fe3O4 magnetic nanoparticles andcoated with SiO2 to prepare magnetic core-shell nanoparticles. Then immobilized Schiff baseof iron and vanadium complexes on magnetic core-shell nanoparticles was prepared as a recoverable magnetic nano catalysts. These catalysts were named Fe3O4@SiO2@L1@Fe, Fe3O4@SiO2@L2@Fe and Fe3O4@SiO2@L3@V. Furthermore,olefines epoxidation, sulfides and alcohols oxidation were studied with using iron and vanadium magnetic nano catalysts. The supported catalysts were characterized by atomic absorption, FT-IR and UV–Vis spectra.The catalytic performance of the synthesized iron catalyst was tested for the epoxidation of cyclohexene, styrene and...

Preparation of Heterogeneous Catalysts by Immobilization of Molybdenum and Manganese-shiff Base Complexes into the Nanopores of Zeolite and SBA-15

, Ph.D. Dissertation Sharif University of Technology Zare, Maryam (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

This thesisconsiders new fundamental approaches to yield heterogeneous catalysts in to three sections. The first section described the immobilization of the molybdenum-Schiff base complexes in pores of SBA-15 in two different methodologies depending on the actual structure of the complexes., (i) stepwise formation of the complex by initial covalent anchoring of one of the components and consecutive solid phase synthesis consisting of the condensation of the other components of the salen complex (iii) one-step complex immobilization by covalent binding through the ligand.Based on the first methodology, we report the preparation of ordered mesoporous silica SBA-15 containing a molybdenum...

Synthesis and Characterization of Various Transition Metal Complexes and the Application in Oxidation, Heck, Suzuki, Sonogashira and Olefin Metathesis

, Ph.D. Dissertation Sharif University of Technology Amini, Mojtaba (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

In nature, catalysis is of vital importance in a wide variety of biochemical processes catalyzed by metalloenzymes. The functions performed by the metalloenzymes and their significance have inspired a range of biomimetic studies, and intense efforts have been concentrated on the synthesis of low molecular weight complexes to model the spectroscopic features of such enzymes. Concomitantly, a challenging frontier in the field of biomimetic chemistry is the development of highly reactive model compounds that are able to effect rapid and selective substrate conversion. Some important catalytic transformations that have gained attention in recent years involve the carbon-carbon coupling, olefin...

Synthesis and Study of Catalytic Reactivity Oxo Vanadium (IV)& (V) Complexes with N,N'-Ethylenebis(Salicylimine)Ligand in Oxidation of Sulfides and Epioxidation of Olfins by Urea Hydrogen Peroxide (UHP) and Tert-Butyl Hydroperoxide (TBHP)

, M.Sc. Thesis Sharif University of Technology Nadiri, Siheila (Author) ; Bagherzadeh, Mojtaba (Supervisor)

Abstract

The selective oxidation of sulfides to sulfoxides is an important method in organic synthesis because sulfoxides are useful synthetic intermediates for the construction of various chemically and biologically significant molecules. To date, the most important method of preparation involves the oxidation of sulfides. Various oxidizing agents are used for this purpose. Oxovanadium(IV)(Salen) and oxovanadium(V)(Salen)Cl were synthesised and screened in the vanadium-catalysed oxidation of sulfides to solfuxides with urea hydrogen peroxide(UHP) as terminal oxidant. Both complexes showed good activity and selectivity trough the catalytic reaction.characterized by elemental analyses, IR, 1H and 13C...

Design and Implementation of Fully Integrated Frequency Synthesizer for Biomedical Applications

, M.Sc. Thesis Sharif University of Technology Aghlmand, Fatemeh (Author) ; Atarodi, Mojtaba (Supervisor)

Abstract

Fully integrated frequency synthesizer is one of the important system-on-chips building blocks. Among this circuit’s remarkable applications, Bioelectronics field is very common. In these applications, advanced microelectronic circuits are used in order to diagnosis and treatment of diseases. The aim of this thesis is design and implementation a wideband frequency synthesizer in a 0.18um CMOS technology. The main usage of this circuit is in a fully integrated implantable biomedical sensory chip. This circuit generates two necessary local signals in sensory chip to stimulus cells and process the information.
Frequency synthesizer is based on phased locked loop (PLL) circuit and produce...